Grafted copolymers of nitrogenous, heterocyclic monomers with polyolefins having pendant ethylenically unsaturated moieties have previously been proposed for use in lubricating oils as viscosity index improving (VII) agents and as dispersants for keeping the insoluble materials in the crankcase of an internal combustion engine in suspension. Among many graftable polyolefins suggested for this use are ethylene-propylene polyolefins, grafted with 0.3% by weight of N-vinylimidazole. U.S. Pat. No. 4,092,255, column 10, lines 52-53. Other examples in the same patent are “statistic” copolymers, which are distinguished from grafted copolymers. U.S. Pat. No. 4,092,255, column 4, lines 5-13.
Another material for use as both a viscosity index improver and a dispersant is a polymer containing N-vinyl pyrrolidone and an alkyl methacrylate. U.S. Pat. No. 4,146,489, column 1, lines 51-62.
Grafted polyolefins for use as lubricating oil additives have been prepared by dissolving the selected polyolefin in a solvent (which may be a lubricating oil base stock), adding an organic peroxide as a free radical generator (also referred to herein as an initiator), holding the mixture at an elevated temperature to form active sites on the polyolefin, adding the graftable monomer, and allowing the mixture to react at an elevated temperature for long enough to form the desired grafted polyolefin. U.S. Pat. No. 4,092,255, column 4, line 54, to column 5, line 12.
The prior art also suggests that the grafting reaction to form a dispersant VII grafted polyolefin can be controlled to avoid by-products by combining the polyolefin, graftable monomer, and initiator at a temperature below the initiation (reaction) temperature of the initiator, then heating the mixture to above that initiation (reaction) temperature to begin the reaction. U.S. Pat. No. 4,146,489. Example 1 of the '489 patent suggests that the initiation (reaction) temperature of di-t-butyl peroxide is between 160° C. and 170° C. Addition of the initiator in two stages is suggested in Example 4 of the same patent. A grafted polyolefin containing 1-10% by weight, preferably 2-6% by weight, most preferably about 3% by weight of the grafted monomer is taught. '489 patent, column 3, lines 11-15.
U.S. Pat. No. 5,523,008 describes a grafted polyolefin containing at least about 13 moles of N-vinylimidazole or other ethylenically-unsaturated nitrogen-containing and/or oxygen-containing monomers per mole of a grafted polyolefin backbone. Also described is a lubricating oil comprising a lubricant base oil and a grafted polyolefin as described above. Also described is a method of making a dispersant-viscosity index improver. N-vinylimidazole or other ethylenically unsaturated nitrogen-containing and/or oxygen-containing monomers and a graftable polyolefin are reacted with enough of an initiator to graft at least about 13 moles of the monomer to each mole of the polyolefin.
U.S. Pat. No. 5,663,126 describes a grafted polyolefin containing one or more of N-vinylimidazole, 4-vinylpyridine, and other ethylenically-unsaturated nitrogen-containing and/or oxygen-containing graftable monomers grafted to a polyolefin copolymer. Also described is a lubricating oil comprising a lubricant base oil and a grafted polyolefin as described above. Also described is a method of making a dispersant viscosity index improver. N-vinyl-imidazole or other ethylenically unsaturated nitrogen-containing and/or oxygen-containing graftable monomers and a graftable polyolefin are reacted with enough of an initiator to graft the monomer to the polyolefin. The initiator and/or graftable monomer is added to the other ingredients, maintained at the reaction temperature, over a period of time. The reaction temperature is maintained at a level high enough to give acceptable reaction times. The monomer and the initiator each can be added at a uniform, relatively slow rate during the reaction. Also described is a method of making a dispersant viscosity index improver using melt reaction conditions. U.S. Pat. Nos. 5,814,586, 5,874,389, and 6,300,289 claim priority through one or more continuations of the application that issued as U.S. Pat. No. 5,663,126 and accordingly have the same disclosure.
Other patents disclose the preparation of dispersant viscosity index improvers by reacting a polyolefin with an acylating agent, and thereafter reacting with an amine so as to form a copolymer having nitrogenous moieties. For example, U.S. Pat. No. 4,320,019 describes reaction products prepared by reacting (a) interpolymers of ethylene, one or more C3-C8 alpha-monoolefins, and one or more polyenes selected from non-conjugated dienes and trienes, with (b) one or more ethylenic carboxylic acid acylating agents to form an acylating reaction intermediate which is further reacted with (c) an amine. These reaction products are said to be useful as multi-functional additives to a variety of lubricating oils for enhancing their dispersancy as well as improving their viscosity-temperature relationship.
U.S. Pat. No. 5,424,367 describes a process for carrying out multiple sequential reactions in a single reactor. A polymer melt is reacted with a first set of reagents to form a grafted functional compound, and thereafter the polymer melt is reacted with a second and different set of reagents to include functionalities that are desired in the final product. The first set of reagents may be unsaturated mono- or poly-carboxylic acids and cyclic anhydrides, salts, esters, imides, amides, nitrites, and other substituted derivatives from said acids. A preferred grafted functional compound is maleic anhydride. The second set of reagents may include alcohols, thioalcohols, and amines, with amines being preferred. Suitable amines include primary amines, N-arylphenylenediamines, aminoperimidines, aminoindoles, aminoindazolinones, and aminomercaptotriazole.